Characterization of novel 3D-printed metal shielding for brachytherapy applicators

To characterize 3D-printed stainless steel metal samples in the presence of an Iridium-192 source for organ-at-risk sparing in gynecologic brachytherapy.

Samples of 3D-printed stainless steel (5.5 × 5.5 cm², thickness range 1-5 mm) were embedded in a solid water phantom at varying distances from source catheters. An Ir-192 brachytherapy source was passed through the phantom and the dose was measured using EBT3 Gafchromic film. The film was initially positioned in the sagittal plane 2 cm away from the catheters, with the metal directly below and then 1 cm from the film. A uniform dose was delivered at the film plane. A second setup measured a depth dose curve in solid water with film in the transverse plane directly above the metal samples. This setup was recreated using Monte Carlo simulations (EGSnrc egs_brachy). Validation between methods was performed with unshielded (solid water only) measurements.

The planar dose passing through the metal samples (thickness 1-5 mm) at the midpoint between the film and catheters, decreased compared to solid water by 7.4% ± 6.9% to 26.5% ± 5.5%. Dose enhancement on the order of 5% was noted when metal was directly adjacent to the film. The average decrease in depth dose from a single dwell position ranged from 10.0% ± 5.9% (1 mm) to 21.1% ± 5.3% (5 mm) as measured with film, and from 3.8% ± 0.9% (1 mm) to 16.3% ± 0.9% (5 mm) using MC simulation. The average depth dose values were measured using a line width of 2.5 mm for film, and 3 mm for MC simulation, and the measurements generally agree within standard error.

The 3D-printed metal samples show potential for personalized applicators. Maximum dose reduction of 26.5% ± 5.5% compared to solid water was measured at 2 cm from the source using the 5 mm sample. An outer layer of solid water could potentially be used to reduce dose enhancement due to increased scatter near the metal.